1. Field of the Invention
The present invention relates to a method for producing a sulfide solid electrolyte material, which can simultaneously achieve microparticulation of a sulfide solid electrolyte material, a high recovery rate thereof and maintenance of an ion conductivity thereof.
2. Description of Related Art
In recent years, as information-related devices such as video cameras and portable telephones and communication devices rapidly prevail, development of batteries used as a power source thereof is gaining importance. Also in automobile industries, development of high-output-power and high-capacity batteries for electric automobiles or hybrid automobiles is under way. At the present time, among various batteries, lithium batteries are gathering attention from the viewpoint of high energy density.
Lithium batteries that are commercially available at the present time use an electrolytic solution containing an inflammable organic solvent. Accordingly, a safety device for suppressing a temperature increase during short-circuiting has to be attached and an improvement in structures and materials for suppressing short-circuiting is necessary. In contrast, a whole solid-state lithium battery in which an electrolytic solution is replaced by a solid electrolyte layer does not use an inflammable organic solvent inside a battery. As a result, it is considered that the safety device can be simplified and the whole solid-state lithium battery is excellent in production cost and productivity. In addition, as a solid electrolyte material used for a solid electrolyte layer like this, a sulfide solid electrolyte material is known.
In order to obtain high-performance whole solid-state batteries, a sulfide solid electrolyte material has to be microparticulated. In Japanese Patent Application Publication No. 2008-004459 (JP 2008-004459 A), for example, a sulfide solid electrolyte microparticles having an average particle size of 0.1 to 10 μm is disclosed. Further, JP 2008-004459 A discloses to use amide, amine salt, or ester, which has an aliphatic alkyl or aryl group, as a dispersion stabilizer when pulverizing a sulfide solid electrolyte material.
A sulfide solid electrolyte material contains sulfur (S). Accordingly, it is a material softer than, for example, an oxide solid electrolyte material. As a result, the sulfide solid electrolyte material tends to form a solid/solid interface and the surface resistance thereof can be advantageously readily reduced. In contrast, since the sulfide solid electrolyte material is a soft material, there is a disadvantage that it is difficult to microparticulate the material. As one of reasons, as described below, granulation occurs simultaneously with pulverization. Further, when a sulfide solid electrolyte material is pulverized by media-type pulverization (ball milling, for example), the sulfide solid electrolyte material adheres to the media to result in low recovery rate of the sulfide solid electrolyte material. In addition, it is considered to use, during pulverization, a dispersing agent to inhibit the sulfide solid electrolyte material from granulating and adhering to the media. However, there is a possibility that conventional dispersing agents cause an ion conductivity of the sulfide solid electrolyte material to deteriorate.